Wafer-level transfer technologies for PZT-based RF MEMS switches

We report on wafer-level transfer technologies to integrate PZT-based radio frequency (RF) microelectromechanical-systems switches on CMOS. Such heterogeneous integration can overcome the incompatibility of PZT material with back-end-of-the-line (BEOL) CMOS technology. The PZT stack and the transfer process have been optimized to avoid degradation of the PZT actuators during the transfer. In particular, we have optimized the seed layer for the growth of highly oriented PZT on a patterned TiO₂-Pt layer, optimized the electrodes structure, and developed an Al₂O₃ capping layer to prevent degradation of PZT during the transfer process. A full wafer-level transfer process and a selective transfer technology allowing the distribution of RF switches from one source wafer to many receiving wafers has been demonstrated. The latest transfer process demonstrated exhibits great potential for cost optimization of wafer-level transfer of microdevices. In a separate experiment, we have demonstrated the BEOL CMOS compatibility of our integration technique. Switch characterization showed insertion loss of less than 0.5 dB and an isolation better than 30 dB for the 0.4- to 6-GHz frequency range with 15-V actuation voltage.